Diesel engines typically have a higher efficiency than gasoline engines due to the increased compression ratio of the diesel combustion process and the higher energy density of diesel fuel. Consequently, diesel engines commonly achieve better gas mileage than equivalently sized gasoline engines. Vehicle manufacturers incorporate emission control devices into the exhaust systems of diesel engines to reduce emissions.
In one conventional method, vehicle manufacturers incorporate particulate matter (PM) filters and diesel oxidation catalysts (DOCs) into diesel engine exhaust systems. A PM filter filters particulates from the exhaust stream. Eventually, the PM filter reaches a capacity and requires cleaning or regeneration. During regeneration, a control module initiates engine control modifications that increase the temperature of the exhaust gases. The increased temperature heats the DOC. When the DOC is at an appropriate temperature, added fuel is injected to further heat the exhaust to the PM filter. At an appropriate temperature, the PM filter burns off the trapped particulates in the PM filter. However, the DOC or other diesel exhaust system components may be adversely affected when the temperature of the exhaust gases departs from an allowable range.